Endocrine System-Chapter 15

-the body's second greatest controlling system with influences metabolic activities of cells by means of hormones. -the hypothalamus has both neural functions and releases hormones -other tissues and organs that produce hormones are adipose tissue, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart.

Pituitary, thyroid, parathyroid, adrenal, pineal, and thymus glands The pancreas and gonads produce both hormones and exocrine products

Chemicals that exert effects on the same cells that secrete them not concidered a hormone since hormones are long-distance chemical signals

Locally acting chemicals that affect cells other than those that secrete them Not considered hormones since hormones are long-distance chemical signals

Chemical substance by cells into the extracellular fluids. - Regulates the metabolic function of other cells - Have lag times ranging from seconds to hours - Tebd to have prolonged effects - Are classifies as amino acid-based hormones or steroids

Biologically active lipids with local hormone - like activity

- Amino acid-based - most common - Amines, thyroxine, peptide, and protein hormones - Steroids - gonadal and adrenocortical hormones

Hormones alter target cell activity by one of two mechanisms: - Second Messengers: - Regulatory G proteins - Amino acid-based hormones - Direct gene sctivation - steroid hormones The precise responce depends on the type of the target cell.

Hormones produce one or more of the following cellular changes in target cells - Alter plasma membrane permeability - Stimulate protein synthesis -Activate or deactivate enzyme systems -Induce secretory activity -Stimulate mitosis

- Hormone (first messenger) binds to its receptor, which then binds to a G protein - The G protein is then activated as it binds GTP, displacing GDP - Activated G protein activates the effector enzyme adenylate cyclase - Adenylate cyclase geberates cAMP (second messenger) from ATP - cAMP activates protein kinase, which then cause cellular effects within the target cell

- This interaction prompts DNA transcription to produce mRNA - The mRNA is translated into proteins, which bring about a cellular effect

- Hormones circulate to all tissues but only activate cells referred to as target cells - Target cells must havee specific receptors to which the hormone binds - These receptors may be intracellular or located on the plasma membrane

Are only found on certain cells of the adrenal cortex

Are found on nearly all cells of the body since it stimulates cellular metabolism

Depends on three factors: - Blood levels of the hormone - Relative number of receptors on the target cell - The affinity of those receptors for the hormone